Aircrafts comprise a de-icing system which during the flight conducts hot bleed air from a propulsion unit to a wing, in particular the leading edges of the wing. As a result, during the flight the wing is maintained at a temperature at which it is ensured that no ice is formed on the wing. As is generally known, ice on a wing may lead to the aircraft crashing. The use of this de-icing system is important, in particular, during the descent of the aircraft. If the aircraft flies at high altitude, for example 10,000 meters, the air has relatively low humidity but is very cold. As a result, the wing of the aircraft is cooled to a low temperature. During the descent, the aircraft may enter more humid air layers. As the wing of the aircraft is still at a temperature of considerably below 0° C., when descending below a height of approximately 7,300 meters (approximately 22,000 feet), ice may form on the wing which may lead to a crash. As mentioned in the introduction, the hot air conducted to the leading edges of the wing has the purpose of heating the wing of the aircraft so that even during the descent no ice may be produced on the wing.
A leaking hot air conduit in a wing may have the result that the wing is not fully de-iced. Moreover, hot air enters the inside of the wing which may damage components in the wing and may impair the structural integrity of the wing.
Hot air at a temperature of approximately 200° C. and above may reduce the strength of a wing of the prior art produced from a metal. It is planned to construct wings of future generations of aircraft from a composite material, in order to reduce the weight thereof. One composite material used is glass fibre-reinforced plastics (GRP), the structural integrity thereof already being reduced at approximately 85° C. As a result, bleed air from the propulsion unit at a temperature of approximately 200° C. has to be prevented from entering a wing produced from a composite material. In a wing produced from a composite material, the entrance of hot air into the wing may have a greater impact on the structural integrity of the wing.
In order to ensure that the wings are reliably de-iced, a pressure sensor, which senses the static pressure in the conduit, and a flow sensor, which senses the volumetric air flow rate, are provided in the conduit. Optionally, a temperature sensor may be provided which senses the temperature of the air flowing through the conduit. If the temperature and the volumetric air flow rate are known, the air mass flow rate may be determined therefrom.
FIG. 1 shows a first characteristic curve 101 of the air mass flow rate over the static pressure in the conduit, if a leak is not present. The characteristic curve 102 shows the static pressure over the air mass flow rate, if a leak is present. As a result of the leak, a new characteristic of the air mass flow rate to the static pressure is produced. There may be a lower static pressure where the air mass flow rate remains the same or a higher air mass flow rate where the static pressure remains the same. However, it is also possible that both variables change. The volumetric air flow rate may be measured and calculated by means of the air temperature of the air mass flow rate.
The characteristic curve between the air mass flow rate and the static pressure is subjected to fluctuations due to manufacturing tolerances of the conduit system to a level of approximately ±5% and above. For example, mounting tolerances in the case of bends and branches in the conduit may influence the characteristic curve of the air mass flow rate and static pressure. If no tolerances are assumed, the system has the characteristic curve 103 shown in FIG. 2. If the maximum error in a first direction is assumed, the system has the characteristic curve 104 and if the maximum error in a second opposing direction is assumed, the system has the characteristic curve 105. If a point or a characteristic curve moves within the range limited by the characteristic curves 104 and 105, a leak is not able to be identified.
FIG. 3 shows the characteristic curve 103, in which no tolerances are assumed. The characteristic curve 104 shows the case in which maximum tolerance in a first direction is assumed and the characteristic curve 105 shows the case in which maximum tolerance in a second opposing direction is assumed. If a point of the characteristic curve 103 moves between the range limited by the characteristic curves 104 and 105, a leak is not able to be sensed. In the example of FIG. 3, the characteristic curve 102 shows a conduit with a leak. As the characteristic curve 102 is located outside the range defined by the characteristic curves 104 and 105, this leak may be sensed. The leak thus has to be of a relatively large volume in order to be sensed. In the example shown in FIG. 3, the operating point 106 of the system is located on the characteristic curve 104, as all components of the system have maximum
tolerance in the first direction. In the case of a leak, the ratio of air mass flow rate to static pressure is displaced to the point 107. It is recognised that the static pressure has to be altered by a high value in order for the leak to be able to be sensed. This may lead to a small leak not being able to be sensed, which may nevertheless lead to the structural problems mentioned in the introduction, not only in wings made of a composite material but also in a wing of the prior art made of metal.
In FIG. 4, the case is shown in which all components of the system have maximum tolerance in the second opposing direction. Thus the operating point 108 of the
system in the normal mode of operation is located on the characteristic curve 105. In the case of a leak, the operating point 107 is located on the characteristic curve 102. The system senses a leak, even with a slight alteration of the static pressure from the value DP1 to the value DP2. Thus it is possible for a small alteration in pressure to be interpreted as a leak.
In FIG. 5, the characteristic curve 103 shows the ratio of air mass flow rate to static pressure, if no tolerances are assumed. The characteristic curve 104 represents the case where all components of the system have a tolerance in the first direction and the characteristic curve 105 represents the case where all components of the system have a tolerance in the second opposing direction. In the case shown in
FIG. 5, the operating point 109 of the system is located on the characteristic curve 104. All components of the system thus have a tolerance in the first direction. In the case of a leak, in the case shown in FIG. 5, the operating point 107 is located on the characteristic curve 102. Said operating point is located within the undetectable range between the characteristic curves 104 and 105, as has been described above. Thus, the system of the prior art is not able to sense a relatively large alteration to the static pressure. Thus problems with the structural integrity of the wing mayresult, as hot air may enter the wing, without this being able to be identified by a system of the prior art.
The problems set forth above may be resolved by more sensors being fitted. This, however, leads to an undesired weight increase, greater complexity, increased maintenance cost and thus additional costs.
It is an object of the invention to provide an aircraft conduit monitoring system which, even with relatively large conduit component tolerances, may identify leaks or other faults.